This invention relates to apparatus for cutting waste materials into smaller pieces, and particularly to apparatus suitable for shredding fiber-reinforced resilient material such as discarded rubber tires.
The disposal of waste materials has become a major problem in modern society as the cost of transportation has risen and the availability of land on which waste materials can safely be disposed has decreased. Many types of material are not readily adapted to disposal in sanitary land fill areas without being shredded into smaller pieces which take up less space. For example, pneumatic tire casings, particularly those reinforced with fiber or wire, are extremely durable, and when in their original form occupy a large volume compared to the actual volume of material of which they are made. Such scrap materials may also contain valuable reclaimable substances yet be uneconomical to transport for reclamation in original form because of their bulkiness and unwieldiness. Shredding such material, then, can increase the rate of decay of discarded material, make more surface area available for chemical reclamation processes, and reduce bulk sufficiently to greatly reduce transportation costs.
Until recently, worn out tires have typically been disposed of by accumulation in huge piles which are both unsightly and very long-lasting. These piles of tires also present fire and health hazards, since when burned such material produces toxic smoke and is very difficult to extinguish, and because water trapped in tires serves as an excellent breeding ground for mosquitoes and other undesirable insects.
As world-wide oil prices increase, recycling of scrap materials formerly wasted has become more economical. For instance, oil can be chemically recovered from used tire rubber. Chemical processes for recovering oil from old tires or for preparing old rubber for reuse, however, require that the surface area exposed to chemical action be increased over that presented by a tire in its ordinary form, and this can be accomplished by cutting tires into small pieces. Ground or shredded rubber products are also useful in the production of skid-resistant highway surfaces and resilient surfaces for running tracks and the like.
The resiliency of rubber, however, and its resistance to abrasion and cutting, especially when reinforced by fiber or wire, have previously made it very difficult to grind tires efficiently enough for the recycling of used tires to be economically worthwhile. Although some previously known devices were capable of shredding lighter weight tires such as some automobile tires, very large tires such as those used on large trucks, tractors and earth moving equipment, even though they contain large amounts of rubber, resisted economical shredding by previously known means. For example, hammermill grinders typically use too much energy in overcoming the resiliency of the rubber to shred or grind tires without a great amount of wasted heat, while slicers having reciprocating sharp-edged blades are typically too slow, and the knife edges of such equipment are susceptible to rapid wear and frequent breakage, and are difficult to sharpen, making such machines inefficient.
Devices such as the apparatus disclosed in Nelson U.S. Pat. No. 3,656,697, which abrasively reduce scrap such as tires to small pieces, additionally have many serious shortcomings which make them uneconomical to use. Abrasive coatings are quick to wear away, and in wearing away they contaminate the shredded material with bits of the abrasive material. This can be a serious problem when shredding rubber or plastics for future chemical reprocessing. Abrasive wheels are initially very expensive, and are also very expensive to maintain and repair. Abrasive reduction of tires as taught by Nelson produces large quantities of wasted heat, often igniting the rubber, with resulting heavy smoke. The abrasive grinding of tires is furthermore a slow process, since the Nelson apparatus merely gradually wears away the rubber surface, with a "V" shaped arrangement of a plurality of intermeshed parallel abrasive discs which retain scrap material within the "V" until it has been reduced to particles small enough to fall between the intermeshed discs.
Recently developed machinery, however, is capable of economically reducing tires and other scrap to smaller sized pieces. In particular, the tire grinding apparatus disclosed in Holman U.S. Pat. No. 3,931,935, Ehrlich et al. U.S. Pat. Nos. 4,052,013 and 4,134,556 and Baikoff U.S. Pat. No. 3,991,944 are all capable of shredding tires. All of these devices include a pair of counter-rotating cylindrical cutter rolls having intermeshing cutter discs which cooperatively shear or tear scrap material between sharp edges of adjacent discs.
A shortcoming common to prior art tire shredding apparatus is that large pieces of material may not initially be caught by the cutter discs of the cutter rolls of apparatus such as that disclosed by Holman, Baikoff, and Ehrlich et al. (in U.S. Pat. No. 4,052,013). Even though most of the above-mentioned apparatus for cutting scrap materials employs tapered feed chutes to position material to be shredded in an appropriate location above horizontally oriented cutter rolls, some materials, such as large tires, may bounce on the tops of the intermeshed cutter rolls for a considerable time before being caught and shredded by the cutter rolls. The lack of positive feed may thus allow scrap material to pile up atop the cutter rolls, rather than proceeding smoothly and continuously through the shredder, and efficiency is reduced, since no material is being shredded during such a blockage. To overcome this problem in prior art scrap shredders it is often necessary to manually position pieces of scrap material such as large tires for acceptance by the cutter rolls, a procedure which is at best labor-consuming, and additionally can be very dangerous.
Another problem of such apparatus as that of Holman is that cutter discs having replaceably attached peripheral cutting edge portions suffer wear of the side faces of the cutter discs radially inward from the replaceable cutting portions. Such worn areas tend to catch cut scrap material, increasing the power required to operate the apparatus and producing additional wasted heat. This occurs particularly when shredding rubber vehicle tires, because of the abrasive nature of tire rubber, steel tire tread belt and bead wire, and the gravel and sand often imbedded in or carried on the surfaces of discarded tires.
Ehrlich et al (556), discloses a plurality of sprocket-like infeed wheels which are located on parallel counter-rotating shafts to propel tires toward the converging portions of the cutter rolls of a tire-shredding machine. While these feeder wheels are helpful, they do not completely solve the problem, since a resilient tire casing can expand, between the feeder wheels and the cutter rolls, to a width preventing the cutter rolls from easily grasping the tire.
Furthermore, the infeed wheels disclosed by Ehrlich may be sufficient for feeding tires of a particular size range into a scrap cutting apparatus, but when the scrap to be shredded includes such articles as discarded steel drums, refrigerator cabinets and similar "white goods", as well as tires varying from three inches to 24 inches or more in tread width, it becomes readily apparent that an infeed mechanism of a fixed size may be very inefficient. What is needed, therefore, is a machanism for positively aligning and feeding scrap articles of widely varying sizes into a cutter mechanism.
Another common problem encountered in cutting apparatus utilizing an intermeshing pair of counter-rotating cutter rolls is that the material which has been cut tends to accumulate between adjacent discs of one or both of the cutter rolls. This problem was early recognized, and one way of dealing with the problem is illustrated in Milne U.S. Pat. No. 1,706,935, which discloses rotary strippers positioned on the discharge side of grass cutting apparatus which is similar in operation to the above-described scrap cutting apparatus of Holman, Ehrlich, and Baikoff. These strippers comprise radially-extending arms which pass between the cutter discs of each cutter roll to strip away cut material. Similarly, Asbill, Jr., U.S. Pat. No. 2,370,129 illustrates use of sawtooth-edged stripper wheels to remove cut material from between the cutter discs of a machine for cutting cotton, corn stalks, tobacco or other fibrous or sheet material, and Holman employs a similar pair of sawtooth-edged stripper wheels in one embodiment of his tire shredding apparatus. While the Holman, Asbill, and Milne machines are thus able to clear themselves, they do nothing to solve the first mentioned problem, that of ensuring that material is fed efficiently to the shredding apparatus itself.
Scrap shredding apparatus has in the past been portably mounted on trailer truck chassis for transport between sites where material to be shredded has been temporarily accumulated. Thus such apparatus may be brought to a local site and operated until the scrap accumulated at that location has been shredded, and the apparatus may then be moved to another site. Known portable shredding machines, however, typically allow shredded material to fall from the shredding apparatus to the ground, where it must later be picked up and loaded into a vehicle for further disposition. This, however, limits the positioning of such a portable scrap cutting apparatus, since access to the same position relative to the apparatus must always be provided so that cut scrap may be collected.
What is needed, therefore, is a portable scrap material cutting apparatus which advantageously orients and positively feeds scrap material such as large tires into the cutting mechanism so as to avoid pileup of scrap material at the point of entrance into the cutting mechanism, and which also strips cut material from the cutter rolls to prevent such already cut material from clogging and overloading the apparatus. It is also desirable to provide a mechanism which is wear resistant, efficient, and not likely to contaminate material being shredded. It would be particularly advantageous for such an apparatus to be portable and capable of conveying shredded scrap to any of various locations relative to the apparatus.